The union of special (SR) and general (GR) relativity. Use this tag if both SR and GR apply.
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199 views
Am I faster than my shadow?
I guess that everything that happens to me (or I do), happens before my shadow "records" the information. Is that right? Is it the same for any observer?
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3answers
92 views
Violation of Newton's 3rd law
I'm just expressing my guess.
Let two particles A and B experiences forces $F_1$ and -$F_2$ between them and let guess also there are two observer, one is stationary and other is moving with ...
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2answers
130 views
What if a normal digital clock used to measure time in twin paradox?
Last night I was watching a youtube video about twin paradox. It still continues to baffle me :).
In that video, the speaker conceptualizes a clock that measures time by reflections of light. If we ...
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2answers
156 views
length contraction question
we know from eintein's theory of relativity that lets say, a ruler is travelling to a speed if light, then we can say that the ruler (from our view as observers) has shorten. but why, lets say we have ...
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2answers
561 views
If nothing in the universe can travel faster than light, how come light can't escape a black hole? [duplicate]
Possible Duplicate:
How does gravity escape a black hole?
If nothing in the universe can travel faster than light, how come light can't escape a black hole? I mean, Einstein's relativity ...
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2answers
127 views
Is a compact universe consistent with the results of (for example) the Michelson-Morley experiment?
If the universe is compact then there is a twin paradox that is resolvable only by selecting a preferred inertial reference frame (arXiv). I was under the impression that the lack of a preferred ...
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2answers
145 views
light travels a maximum speed… /? [duplicate]
Possible Duplicate:
Is it possible for information to be transmitted faster than light?
we know that speed of light is an unconquerable term in physics..light takes about 1 year to travel ...
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2answers
226 views
The Lorentz Transformations in the Micro-World
Two particles[or micro-observers] A and B are in relative uniform motion wrt each other in the x-x’ direction. The “observer” A decides to deduce[or interpret] the Lorentz Transformations wrt to B. ...
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1answer
125 views
Why can't we accelerate objects past the speed of light? [duplicate]
Is there any intuitive reasoning behind why there would be this universal speed limit? It just seems so arbitrary. I know that there must be things that are unknown, but what reasoning is there behind ...
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3answers
102 views
Black hole accretion of dark energy
Dark energy physically can be interpreted as either a fluid with positive mass but pressure the negative of its density (pressure has units of energy/volume, and energy is mass), or a property of ...
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2answers
191 views
Photons in a gravitational field
I have been really staring for a while in a MP-Beiser book and I totally disagree with a statement he does there. On a page 85 he states that photons act as they have a mass $m$. He derives this by ...
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2answers
79 views
Causal reconnection
Can causally disconnected regions join up again? For example the universe is expanding faster than light creating cosmological horizon, but what if something causes the expansion to slow down and ...
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2answers
98 views
What is the mass of a photon moving at the speed of light? [duplicate]
What is the mass of a photon moving at the speed of light?
And if it does not have mass, how is it affected by gravity?
Also why does Einstein's general relativity support that a gravitational wave ...
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1answer
93 views
Deriving infinitesimal time dilation for arbitrary motion from Lorentz transformations
I'm trying to derive the infinitesimal time dilation relation $dt = \gamma d\tau$, where $\tau$ is the proper time, $t$ the coordinate time, and $\gamma = (1-v(t)^2/c^2)^{-1/2}$ the time dependent ...
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1answer
101 views
Light orbiting a massive body [duplicate]
Possible Duplicate:
Can a photon be made to orbit a known (or undiscovered theoretical) body?
How massive would a black hole have to be for light to orbit it at 1km away from the ...
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1answer
69 views
At what rate does radiation exposure occur at high-c speeds?
If a future astronaut travelled to Alpha Centauri at a significant percentage of light-speed?
Apart from increased blue shifted radiation from their direction of travel - how would they experience ...
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1answer
95 views
Showing that a given matrix provides the desired Lorentz transformation
I am working on problem 5.12 in Halzen and Martin’s Quarks and Leptons. We are asked to show that the matrix
$$ S = 1 - \frac{i}{4} \sigma_{\mu \nu} \varepsilon^{\mu \nu} $$
represents the ...
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0answers
10 views
1D Kinematics - Relative Motion involving non-inertial frames of reference
I recently came across a question involving non-inertial frames of reference. I didn't quite understand the way it had been solved due to some conceptual confusion regarding certain deductions made to ...
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0answers
48 views
Homework Help Please? [closed]
An electron is accelerated from rest through a voltage drop of .13 MeV, and then travels at constant velocity.
a. How long does it take the electron, after it has reached its final velocity, to ...
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1answer
66 views
Spacetime and Timelike Intervals
The difference between a “timelike” spacetime interval and a “spacelike” spacetime interval can be understood in the following way: If the spacetime interval between two events is timelike, there ...
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2answers
52 views
Relativity Problem Given Rest Length and Proper Time
A relativistic train with a rest length of 500.0 m takes 780 ns to pass a stationary observer
standing on the train platform, as measured by the stationary observer.
(a) What is the speed ...
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2answers
46 views
Relativity Problem with Three Reference Frames
I'm having trouble with the understanding on this last problem from my homework set.
Two cars playing demolition derby are moving towards each other with constant velocity,
as measured by ...
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0answers
41 views
Ricci tensor question
Suppose the Ricci tensor $R_{a}^{\;\;b}$, considered as a linear map on $T_{m}M$ at an even $m$, has only real eigenvalues. What are the five possible Jordan forms of $R_{a}^{\;\;b}$? Show that the ...
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0answers
41 views
What is an example of a situation where Quantum Mechanics and Relativity do not work together? [duplicate]
I've learned special relativity in school last semester, and this semester we began learning about Quantum Mechanics, and my teacher told us that there was a Relativistic Schrodinger equation.
I was ...
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0answers
37 views
Need help with relativistic dynamics
I understand the concept, but I'm having a hard time applying the consequences of conservation (energy/momentum). For example:
A proton with kinetic energy 437 MeV hits a proton at rest elastically ...
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0answers
16 views
Period of Transmission of signals in different frames
A radar transmitter (T) is fixed to a system $S_{2}$ which is moving to the right with speed v relative to system $S_{1}$. A timer in $S_{2}$, having a period $\tau_{0}$ (measured in $S_{2}$) causes ...
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0answers
52 views
A Mathematician Who Wants to Learn Particle Physics [duplicate]
Possible Duplicate:
Book recommendations
I'm a grad student in pure math, wrapping up a thesis in Lie theory. After years of talking to mathematicians and physicists, I've decided that it's ...
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0answers
123 views
What facts and examples should I use in a debate with a Relativity Denier? [closed]
I have been asked to 'defend Science' at a Creationist event in Minneapolis, MN, and the guy I'll be debating is against 'Einsteinian Relativity', or as he characterizes it, the idea that there is no ...
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0answers
55 views
Space-time & solar mass
Does the space-time curvature described by Einstein have any affect on the accuracy of our determination in the age of a star or globular cluster? How does this affect our interpretion of how old we ...
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0answers
69 views
Relativity at the bus stop [closed]
This happened to me last week. So I was at my university waiting for the bus. Now there are two buses I can take, let's just call them Bus A and Bus B.
Let's assume the number line is the path of the ...
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0answers
38 views
Why has the ether been disregarded as a valid medium through which light can propagate? [duplicate]
Possible Duplicate:
Ether theory acceptance
Although the Einstein's theory of relativity seemed to make the concept of an ether obsolete, did it necessarily invalidate it? Are there any ...
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1answer
337 views
Time traveling and Time dilation within a multiplayer videogame [closed]
First thing first, I'm looking to implement this within a multiplayer videogame as a "special" skill or powerup, but, I'm willing to build it upon a physics based explanation/theory.
The question may ...
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0answers
103 views
Can space-like fields not commute and still forbid faster-than-light signalling? [duplicate]
Possible Duplicate:
Is microcausality necessary for no-signaling?
If we try to measure two non-commuting observables, only the earlier measurement would be valid. The later measurement ...
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0answers
235 views
How to formulate Lorentz invariance without the temporal dimension? [closed]
The role of "time" in fundamental physics has changed a lot in recent decades. Some physcists believe time is an emergent property rather than a most fundamental parameter of nature laws.
However, ...
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6answers
180 views
Inertial Frames of Reference - Inertial vs. Accelerated Frames
According to Robert Resnick's book "Introduction to Special Relativity", a line states the following as the definition of an inertial frame of reference: "We define an inertial system as a frame of ...
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0answers
18 views
Finding Velocity for Equal Received Wavelength from Two Moving Objects Emitting Light [closed]
In the diagram below, Spaceship 1 and Spaceship 2 are traveling towards earth from
opposite directions. Both spaceships have headlights which emit light, which, when measured in
the reference ...
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1answer
104 views
How do photons experience time? [duplicate]
I know that as velocity approaches the speed of light the time dilation shoots to infinity as shown below.
1)So I want to know how time is perceived from the point of view of the photon?
2)Since ...
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2answers
99 views
The relativistic mechanics of a battery that is being charged and accelerated at the same time
This might be an interesting question:
Let's attach a battery into one end of an electric cable. Then we rotate the battery around, with accelerating speed, using 100 Watts of power, while the ...
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2answers
96 views
Repulsion does not exist; Gravity assist slingshot as a repulsive force [closed]
unification theory might say that there is only one force in universe that is called gravity(attraction).
So at atomic level for same charges that repel eachother(electrons etc.), if thought of as a ...
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2answers
122 views
frames of reference [duplicate]
Possible Duplicate:
Help Me Gain an Intuitive Understanding of Lorentz Contraction
Frames k and k' are inertial frames. Frame k' is moving at a velocity of magnitude v relative to frame k ...
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0answers
41 views
effect of gravity on chemical reaction rates [closed]
a chemical reaction is done on earth in very vacuum and that chemical reaction is also done in space so that gravity higgs field not affect that reaction.
Which reaction will be fast wrt gravity and ...
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1answer
202 views
Why are we talking about space curvature as if we know what space is? [closed]
1) Why are we talking about space curvature as if we know what space is?
Every question about gravity seems to evoke an answer involving "space curvature" which seems like an undefined placeholder ...
